This invention is concerned with power operated tools for driving fasteners into work with the application of a single stroke, and particularly to the driving of fasteners such as nails and staples and the like. Said fasteners are driven with an explosive action that severs each individual fastener from a "stick" supply thereof fed through a magazine and into the head of the tool. Heretofore, it has been thought necessary to provide guide means in the head to guide the penetrating shanks of the fasteners, as they enter the work and until the crown of the fasteners leave the head. And, despite all precautions and ingenuity in head design, there remains the ever present probability, with prior art design, of a jamming due to imperfect fastener formation. For example, there are such fastener driving tools wherein the head is provided with a gate for access to the driveway in order to clear the often expected jams. Accordingly, it is a general object of this invention to provide a fastener guiding head which is virtually non-jamming.
Fastener guiding heads for power tools of the type under consideration have been characterized by front and back plates secured together over the feed end of a magazine to which a power operated driver blade is related by a cylinder and piston means to drive fasteners through a channel formed between said front and back plates. The front plate is essentially a flat cover that closes the channel formed coextensively between the top and bottom of the back plate. A feature of this conventional prior art head construction is the opening through the back plate, said opening being in alignment with the magazine to receive fasteners into the driveway channel where each successive fastener is sheared from the stick thereof to be simultaneously guided by the two head plates and advanced toward the work. Accordingly, prior art back plates have been provided with a guide portion below the points of the fasteners held in stick formation by the magazine, said guide portion forming an extension of the head to a driving plane substantially below the magazine, for clearance. Despite design and engineered precautions, this lower portion of the back plate retained as a guide, often becomes an obstruction to imperfect fasteners, as is evident by the repeated malfunctions wherein the points of the fasteners seek a course behind the back plate rather than through the driveway channel thereof. Needless to say, such a malfunction is destructive of the tools as it causes overstress and deformations, as well as perforations through the magazine walls. Therefore, it is an object of this invention to remove and omit the said lower guide portion of the prior art back plate without loosing the fastener guiding capability of the head.
Heretofore, there has been a transfering of individual fasteners sheared from guided engagement with the next remaining fastener of the stick supply, to guided engagement with the aforesaid lower portion of the back plate and complementary opposing portion of the front plate. In this respect, it is not uncommon that the lower guide portion of the back plate is of a height greater than the length of the fastener, in which case there is a complete severance of the fastener from the stick supply before initial entrance through the driving plane and into the work. And, it is this extended nose portion of the head which has made unobvious the advantages of the present invention as it is disclosed herein. Accordingly, it is an object of this invention to establish initial entrance of the fastener points through the driving plane and into the work prior to disengagement of the severed fastener from the next remaining fastener of the stick supply. With the present invention, the lower portion of the back plate is of reduced height not to exceed the length of the fastener and preferably substantially less than the fastener length, whereby the fastener points are guided simultaneously by means of work penetration and before removal from guided engagement with the stick supply.
The magazines of prior fastener driving tools have been provided with rails and plugs thereof confined to the magazine per se and stopping short of the driveway through which the driver blade travels. Significant also is the termination of the magazine behind and fitting the back plate above its conventional lower driveway portion that forms an obstructing bridge across the head. As stated above, it is an object to remove and/or omit this lower "bridge" portion, but without losing the guideway function so necessary in delivering the fasteners in alignment with the driveway. With the present invention, the plug and/or forward end of the magazine enters the back plate opening to replace the prior art bridge member and thereby form the back of the driveway to guide the crown of the fastener and the driver blade as well. Note that the shanks of the fasteners depend free from the stick supply until re-stabilized by penetrating into the work. Also note that the crown is guided throughout the driving operation. The front cover plate remains unchanged, but with no requirement for an access gate, since jams are now eliminated.
The concept herein disclosed is generally applicable to fasteners including tacks, nails and staples. However, it is the latter staple configuration of fastener which is particularly troublesome, since there is a tendency for the two legs or shanks thereof to be twisted or misaligned. Accordingly, the lower "bridge" portion of prior art back plates have been characterized by spaced guide rails beveled so as to redirect the points of the spaced shanks into the channel-shaped driveway. However, as stated above, this guide rail configuration of the lower "bridge" portion is not always effective, as for example when the fastener imperfection is too great and the points progress and take a malfunctioning course behind said guide rails. It is these spaced guide rails which are also removed and omitted in practicing the present invention, it being an object to reduce the back plate to its very basic requirements by eliminating entirely any obstruction ahead of the fastener as it is delivered through the driveway.